Diarrhea accompanied by blood in stool may be ulcerative colitis and other inflammatory stimulation of intestinal mucosal bleeding, but also may be intestinal polyp rupture bleeding, intestinal cancer tumor rupture bleeding, etc. Diarrhea accompanied by hemorrhoids, etc. will also appear blood in stool. 1. Ulcerative colitis, Crohn’s disease, etc. Due to inflammation stimulation, gastrointestinal tract peristalsis accelerated, diarrhea will occur, inflammation surface damage may also appear blood in the stool, accompanied by mucus. 2. Intestinal polyps may also have diarrhea, intestinal polyps with rich blood flow may rupture and bleed under the pressure and stimulation of intestinal feces, etc. Blood in stool will appear, but most of them are black stools, and when there is a large amount of bleeding, it may be bright red blood stool. 3. Bowel cancer can also cause diarrhea due to the damage of intestinal mucosa by cancer cells and the disturbance of intestinal flora, etc. Blood in stool can also occur due to the erosion of tumor, and most of them are accompanied by the change of stool shape. 4. If diarrhea is accompanied by hemorrhoid flare-ups and other diseases, blood in stool will also occur, usually the blood adheres to the surface of stool, the blood color is bright red, and sometimes there is a feeling of wanting to defecate again and again due to perianal irritation. There may be other reasons for this phenomenon, and you should consult a doctor to find out the cause of the problem and treat it in time so as not to delay your condition.